Receiver signal paths, or channels, of electronic data collection systems (such as airborne electronic receiver systems for unknown input signal spectrums) are often prone to multiple, dynamic sources of distortion that color the channel due to a temperature-time varying environment. As a received signal moves from the antenna through RF (radio frequency) amplifiers, distribution networks, switches and tuners, signal distortions may appear in terms of both frequency and time. The channel distortions may introduce nonlinear effects on the signal's magnitude and phase, especially across the IF (intermediate frequency) filter passband, which color the waveform signature and can affect signal measurement accuracies in time and frequency.
Where the sources of the collected input signals across the receiver wideband spectrum are expected to be unknown before reception, as is the case with respect to passive wideband electronic surveillance receivers, any attempts to equalize the channel must be performed without apriori knowledge because the signal sources, in all respects, are unknown. Furthermore, situations involving receipt of low-probability-of-intercept (LPI) type emitters demand measurement accuracies both at the time of the intercept and instantaneous frequency coincidence of the intercept, usually off band center, thereby stressing the need for low distortion spectral response characteristics across the passband of the passive wideband surveillance receiver. Traditional solutions for channel equalization have failed to adequately handle distortions caused by environmental parameters, such as temperature and other operational conditions.